Fuel trims and timing

[KeltonDSMer]

Do fuel trims, (1G) affect ignition timing advance? I always re-set my ECU befroe tuning. Then, even if I tune for no knock at all, my Low and high fuel trims max out after a week or so at 118% ('90). After this, I notice only about 16degrees advance at the top of the gear. Before the trims max out, it tops at about 18-19 degrees.

I know the car is not knocking, for I am witnessing this while someone is staring at the datalogger.

I've heard that duty cycles can affect timing as well, this only happens when the D.C. goes above 85%....if I pull out fuel and turn doen the boost, it doesn't pull the timing at the top of the gear.



I really want to figure this out, because the 50trim has some lag and the '90 exhaust cam makes things pretty unexciting above 6K, I need all the advance I can get to make it wrothwhile reving to the top of the gear.

Thanks guys,
-Kelton

[KeltonDSMer]

Anyone? Is my timing being puled because of high duty cycles, airflow, or the fuel trims?

[sbiggi]

before you go tuning for wot you need to tune and get your fuel trims all around 100%. The fuel trims affect the wot fuel delivery as well, so if you tune after resetting and trims change that much, you are just waiting your time.

[KeltonDSMer]

See, that's the thing. I can't get the trims to go to 100%, even if I tune on the very rich side for no knock at all, the ECU still wants to add fuel.

[sbiggi]

the trims take a while to move.... first tune the low trim, which can be done idling, use that setting for 1000 rpm on the low settings. then you need to add fuel through out the rest of the rpm band, but those setting will take a while to move. Once you get the trims all around 100% +-10% you can start tuning for wot. The high fuel trim will take a long time to move.

One thing you can watch is the o2 trim, its a realtime indicator of what the ecu is going to do with the fuel trims. It will move alot while driving around. Do not use it when decelerating or going wot. As soon as you go close loop, it will show 100%.

Also, are you sure you have your afc settings correct? the low point should be 30% and the high point should be 80%.

I suck at explaining this.... so I recommend starting with settings from road races site, and going from there.
http://www.roadraceengineering.com/newafc.htm
http://www.roadraceengineering.com/newafcsetting.htm

[KeltonDSMer]

My settings are at 27% and 78% because my turbo starts spooling significantly after 25% so I wanted the extra fuel. The 50trim also spools 10psi at anything higher than 40% at higher engine speeds, so I wanted the extra fuel sooner.

It is just hard to undertand why the trims are moving at all in the first place. I am tuned very rich until I can get to the dyno to lean it out safely, I don't see ANY knock throughout the entire RPM range at WOT. Why would the high trims be adding even more fuel after time? The once, the high trim moves up, I see about 22degrees timing peak after the turbo spools and then it is pulled to about 17 degrees at the top of third.

Thanks for your help,
-Kelton

[sbiggi]

My settings are at 27% and 78% because my turbo starts spooling significantly after 25% so I wanted the extra fuel. The 50trim also spools 10psi at anything higher than 40% at higher engine speeds, so I wanted the extra fuel sooner.

It is just hard to undertand why the trims are moving at all in the first place. I am tuned very rich until I can get to the dyno to lean it out safely, I don't see ANY knock throughout the entire RPM range at WOT. Why would the high trims be adding even more fuel after time? The once, the high trim moves up, I see about 22degrees timing peak after the turbo spools and then it is pulled to about 17 degrees at the top of third.

Thanks for your help,
-Kelton

Your timing will peak then fall a couple degrees by 7000 rpm, especially if you have the 90' ecu. Thats just the way they came from the factory. 91+ will hold more timing, but they will still fall off unless you modify the timing maps.

I think I also read that if/when you hit 2000 hz Karmen the ecu will pull a couple of degrees of timing.

[KeltonDSMer]

Wow, that helps a lot. I sure do have a '90 ecu.....with 125K on it.

I probably see 2000Hz on the AFC before the signal is molested. This means my ECU is seeing a lot because I have pretty high positive values on the AFC. The ECU is probably seeing way too much airflow for it's comfort.

As a matter of fact, the logger stops reading at 1600Hz and it hits that before the WG even opens.

[sbiggi]

Wow, that helps a lot. I sure do have a '90 ecu.....with 125K on it.

I probably see 2000Hz on the AFC before the signal is molested. This means my ECU is seeing a lot because I have pretty high positive values on the AFC. The ECU is probably seeing way too much airflow for it's comfort.

As a matter of fact, the logger stops reading at 1600Hz and it hits that before the WG even opens.


1606hz is the max the logger can show for some reason.

Do you have bigger injectors yet? I hope you do cause I'm maxing out my 450's with a 14b.... I hit 95-100% dtc, and a 50 trim is alot bigger then a stock turbo.

[KeltonDSMer]

Yep, 550's.

I think I will experiment with some higher base fuel pressure when I get around to installing my AFPR. I think the RC injectors would have a better spray pattern at, say, 40-43psi compared to the low FP of the 1G turbos. It would give me a little more room to work with as well.